The present invention relates generally to spindle drive mechanisms with circulating balls and more particularly to a mechanism wherein a spindle provided with an external thread, a spindle nut provided with an internal thread of equal pitch, and balls for transmitting axial forces between the spindle and the spindle nut are arranged with the balls within ball ducts formed by the internal and external threads. Means are provided to enable return of the balls from an outlet of the ball ducts to an inlet thereof with relative rotation between the spindle and the spindle nut operating to effect transmission of axial forces therebetween as the balls are circulated through the mechanism.
Spindle drives of this type are generally distinguished by the fact that they display low frictional resistance characteristics and relatively insignificant wear while allowing positioning of the structural components to be shifted with exactness and without play. The adjustment of an initial tension between the spindle and the spindle nut is of primary importance when the device is used as a feed device in connection with precision machine tools. In such devices, it is important, on the one hand, to ensure that the feed is accomplished without vibrations and rattling and, on the other hand, to eliminate reverse play when the feed direction is changed.
Spindle drives of the type mentioned above are known in the prior art. In such spindle drives, a spindle nut is formed from two parts which are arranged axially behind one another on the spindle and which are clamped together upon the spindle until any existing play is compensated or until a desired initial tension or pressure between the parts is achieved. An example of this type of construction is known from German Offenlegungsschrift No. 1,936,546. However, in all known constructions, having two-part nuts, the adjustment of the play or of the initial tension of the device is effected such that, with the parts of the nuts arranged rigidly against rotation relative to each other, their axial spacing is adjusted and fixed. Alternatively, with the partial nuts locked relative to each other in the axial direction, the partial nuts are arranged so as to be rotatable relative to each other and fixed in their angular positions wherein one of the partial nuts will always rest through the balls against one flank side, with the other partial nut resting against the other flank side of the spindle thread.
Arrangements having two partial nuts usually require a complicated structural configuration and assembly and they are, therefore, rather expensive. In addition, the structural length of such a device is relatively large so that they tend to require a relatively large space for assembly. Additionally, unavoidable pitch error of the spindle will have the effect of creating disadvantages in the operating characteristics which become more pronounced with larger lengths of the entire spindle nut. A further disadvantage of large structural lengths is the resulting high elastic deformation which occurs in the axial direction.
The present invention is directed toward the task of providing a structural arrangement for a spindle drive mechanism of the type discussed above which, when compared with known structures, will be relatively less complicated in its design and assembly and will exhibit a shorter structural length.